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BDS3 - CDS > Radiology > Flashcards

Radiology Flashcards

1
Q

types of misleading shadows on radiograph

A
  • cervical burnout
  • beneath amalgam restorations
  • mach band effect
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2
Q

cervical burnout

A
  • triangular shaped radiolucency at neck of teeth
  • x ray only passes through dentine
  • less attenuation so darker corresponding area on radiograph as more of the beam passes through
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3
Q

misleading shadow beneath amalgam

A
  • consequence of zinc and silver ions released into underlying dentine
  • this increases its radiodensity and radiopaque zone visible
  • other dentine might appear more radiolucent in contrast
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4
Q

mach band effect

A
  • optical illusion caused by the retina
  • makes bright areas look brighter and dark areas darker
  • to enhance contrast and differentiate structures
  • linear in shape
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5
Q

y of ennis

A

superimposition of the nasal cavity floor and anterior margin of maxillary sinus

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6
Q

curve of spee

A

curvature of mandibular occlusal plane

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7
Q

curve of wilson

A
  • across arch curvature…post occlusal plane
  • concave mandibularly
  • convex maxillary
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8
Q

sphere of monson

A

curve of wilson and spee simultaneously demonstrate sphere of monson

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9
Q

occlusal views upper

A
  • anterior oblique maxillary
  • lateral oblique maxillary
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10
Q

occlusal views lower

A
  • true mandibular occlusal
  • anterior oblique mandibular
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11
Q

radiograph aim

A
  • identify presence or absence of disease
  • provide info on nature and extent of disease
  • to monitor disease
  • to investigate unerrupted/missing teeth
  • enables differential diagnoses
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12
Q

radiograph optimum viewing conditions

A
  • low level of light
  • minimise or diminish screen glare
  • utilise monitors with good resolution and brightness
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13
Q

intra-oral views

A
  • bitewings
  • periapicals
  • occlusals
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14
Q

periapicals summary

A
  • show individual teeth and the tissues around apices
  • gives detailed info on teeth and surrounding bone
  • mainly used for detection of periapical pathology and bone levels
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15
Q

key anterior maxillary anatomy on radiograph

A
  • maxillary sinuses
  • nasal septum
  • nasal cavity
  • palatine suture
  • incisive foramen
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16
Q

key posterior maxillary anatomy on radiograph

A
  • zygoma
  • maxillary tuberosity
  • pterygoid plate
  • hamular process
  • max. sinus
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17
Q

key anterior mandibular anatomy on radiograph

A
  • lingual foramen
  • thicker bone of mental protuberance
  • vascular canals
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18
Q

key posterior mandibular anatomy on radiograph

A
  • mental foramen
  • oblique ridge
  • margins of inferior alveolar canal
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19
Q

types of intra-oral radiographs and their subtypes

A
  • bitewings: horizontal & vertical
  • periapical: paralleling & bisected angle
  • occlusal: maxillary & mandibular
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20
Q

benefits of intra-oral radiographs

A
  • high resolution = high detail/sharpness
  • minimal superimposition of other anatomy
  • fast exposure
  • low adiation dose per image
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21
Q

negatives of intra-oral radiographs

A
  • limited to imaging of a small area
  • relatively invasive for patient
  • relatively difficult technique
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22
Q

intra-oral receptor sizes and what type of radiograph

A
  • commonly labeled 0 - 4
  • size 0 = anterior periapicals or bitewings if young child unable to tolerate size 2
  • size 2 = bitewings and posterior periapicals
  • size 4 = occlusals
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23
Q

what does the term projection geometry refer to

A
  • relates to the positioning of all the components involved in taking a radiograph: X-ray beam, subject and receptor
  • perfect projextion geometry should result in a fully accurate, undistorted image
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24
Q

projection geometry - ways an image can become distorted

A
  • X-ray beam is divergent so magnification of image occurs
  • subject not perpendicular to X-ray beam will result in shortened image
  • if receptor not perpendicular to x-ray beam then image will be elongated
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25
Q

ways to achieve best possible projection geometry

A
  • sufficient focus-to-skin distance (larger distance = less divergent beam)
  • position receptor as close to tooth as possible
  • ensure receptor is as stable as possible in mouth
  • use image receptor holders with a beam aiming device
  • keep patient still
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26
Q

focus to skin distance and guidance

A
  • a larger fsd will reduce magnification of the image
  • UK guidance recommends 200mm for intra-oral X-ray units (20cm)
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27
Q

how is focus to skin distance maintained and measured

A
  • distance is maintained by using a spacer cone: fixed or detachable
  • measured from the X-ray source which is marked on the X-ray unit usually as a black dot
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28
Q

bitewings aim to show

A
  • posterior teeth only
  • premolars and molars
  • max and mand teeth at the same time
  • inter-dental bone
  • can be vertical to show more of the roots and alveolar bone
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29
Q

bitewing indications

A
  • detection/monitoring of caries
  • assessment of dental restorations
  • detection/monitoring of periodontal bone loss (less indicated)
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30
Q

paralleling periapical radiographs aim to show

A
  • 1-4 teeth
  • only either maxillary or mandibular teeth
  • entire crown
  • entire root
  • alveolar bone
  • nearby anatomical structures eg floor of max sinus or mental foramen
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31
Q

periapical indications

A
  • detection of apical inflammation
  • detection/monitoring of periodontal bone loss
  • assessment of unerupted teeth
  • assessment of root morphology for extraction/other tx
  • evaluation of endodontic treatment
  • assessment after dental trauma
  • planning/monitoring dental implants
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32
Q
A
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33
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34
Q
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35
Q
A
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36
Q

projection geometry of bisecting angle radiographs and occlusal radiographs

A
  • xray beam not perpendicular to long axes of tooth or receptor
  • long axes of tooth and receptor not parallel to one another
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37
Q

describe bisecting angle technique

A
  • tooth and receptor are tilted at equal but opposite angles
  • if tooth not perpendicular to source image shortened and if receptor not perpendicular image stretched
  • with this technique the two effects counteract one another
  • image has adequately correct dimensions
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38
Q

when is bisecting angle technique used

A
  • when unable to position receptor parallel to tooth
  • if pt has shallow hard palate or lingual sulcus
  • young child struggling to tolerate receptor in mouth
  • tender tooth preventing biting on receptor holder
  • edentulous patient
  • applies to most occlusal radiographs and receptor is not parallel to teeth (lies in occlusal plane)
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39
Q

bisecting angle technique step by step

A
  1. place receptor as close to subject as possible without bending
  2. estimate the angle between the long axis of subject and receptor
  3. bisect this angle with an imaginary line
  4. aim the X-ray beam perpendicular to this bisecting line
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40
Q

what equiptment to use for bisecting angle technique for periapical radiography

A
  • use holder whenever possible
  • patients finger is a last resort
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41
Q

benefits of holders

A
  • avoid radiation dose to hands
  • reduces chance of receptor shifting in mouth
  • some types will guide positioning of X-ray beam
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42
Q

bisecting angle technique benefits vs paralleling for periapicals

A
  • receptor position potentially more comfortable for patients
  • position slightly simpler and quicker
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43
Q

bisecting angle technique downsides vs paralleling for periapicals

A
  • estimating Xray beam angulation can lead to varying degrees of image distortion
  • image hard to reproduce
  • increased risk of irradiating thyroid gland
  • altered positions of some anatomy
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44
Q

occlusal radiographs main types

A
  • upper: anterior oblique maxillary occlusal & lateral oblique maxillary occlusal
  • lower: anterior oblique mandibular occlusal & true mandibular occlusal
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45
Q

occlusal radiogaphs receptor size and position

A
  • normally size 4
  • positioned in occlusal plane
  • faces up or down depending on which jaw is being imaged
  • orientation dependant on size of mouth and patient tolerance
  • once in position patient bites down to hold receptor in place
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46
Q

biting instructions for occlusal radiographs

A
  • ask to bite gently
  • watch for chewing/clenching
  • can add a protective layer to prevent/reduce damage from biting…cardboard or plastic
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47
Q

occlusal radiographs vs other intra-oral radiographs

A
  • allow visualisation of the dentition/jaw from a different angle
  • useful for localising unerupted teeth and investigating root/alveolar fractures
  • slightly larger image of the dentition/jaws
  • can be used if pt cannot tolerate periapical holder
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48
Q

anterior oblique maxillary occlusal positioning

A
  • align occlusal plane parallel to floor
  • place receptor against upper occlusal plane, centrally in mouth
  • get pt to bite gently
  • position x ray tubehead in midline, aiming down through bridge of nose at receptor, at 65 degree angle to receptor
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49
Q

lateral oblique maxillary occlusal positioning

A
  • align occlusal plane parallel to floor
  • place receptor against upper occlusal plane towards side of interest
  • long axis of receptor aligned antero-posteriorly
  • aim xray tubehead through cheek at receptor at 45-55 degree angle to receptor
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50
Q

maxillary occlusal radiograph function

A
  • investigating unerupted/ectopic teeth
  • investigating root fractures
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51
Q

true mandibular occlusal positioning

A
  • place receptor against lower occlusal plane
  • get patient to bite gently
  • tilt head back as far as comfortably possible
  • position xray tubehead perpendicular to receptor aiming upwards under chin
  • do not use rectangular collimation
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52
Q

true mandibular occlusal function

A
  • investigating sialolith in submandibular ducts
  • investigating bucco-lingual expansion of the mandible and position of teeth
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53
Q

anterior oblique mandibular occlusal positioning

A
  • align occlusal plane parallel to floor
  • place receptor against lower occlusal plane
  • get patient to bite gently
  • position xray tubehead in midline aiming up through chin at 45 degree angle to receptor
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54
Q

when to use a smaller receptor for occlusals

A
  • young children too small for larger receptor
  • adults unable to tolerate larger receptor
  • small area of interest
  • use size 2 instead
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55
Q

when may thyroid shields be required

A
  • whenever thyroid gland is in the primary xray beam
  • maxillary occlusal radiographs
  • bisecting angle technique of maxillary anterior teeth
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56
Q

important radiation legislation

A
  • ionising radiation regulations 2017 IRR17
  • ionising radiation (medical exposure) regulations 2017
  • enacted under the health and safety at work act
  • ICRP (International Commission on Radiological Protection) principles
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57
Q

what is ICRP and their main principles

A
  • International Commission on Radiological Protection
  • all radiation exposures should be:
  • justified - do more good than harm and benefit
  • optimised - ALARP
  • limited - individual radiation dose limits used to ensure no person recieves unacceptable level of exposure
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58
Q

what is IRR17
enforced by?
who is responsible

A
  • deals with occupational exposures and exposures of the general public
  • enforced by health and safety executive (HSE)
  • employer responsible for compliance - NHS/private practice owner
  • employees responsible for following safety arrangements - HSE registration required by dentists for use of a radiation generator
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59
Q

what is IRMER17
enforced by?
who is responsible

A
  • deals with medical exposures of patients
  • enforced by healthcare improvement Scotland
  • applies to a variety of medically-related exposures - diagnoses, asymptomatic pts and carers/comforters
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60
Q

what radiation legislation covers carers and comforters
define carer/comforter

A
  • IRMER17
  • individuals who are knowingly and willingly exposed to ionising radiation through support and comfort of those undergoing exposure
  • individuals not those doing so as part of their employment
  • commonly relatives or friends of those undergoing exposure
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61
Q

define controlled area and its dental application

A
  • defined as area around the X-ray source equiptment
  • depending on risk assessment and workload levels
  • for intra-oral units usually 1.5m from source
  • for cone beam CT entire room normally a controlled area
  • no-one should enter this area during exposure unless special procedures are in place
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62
Q

times when non-medical imaging required using medical radiological equiptment

A
  • health assessment for employment purposes
  • health assessment for immigration purposes
  • health assessment for insurance purposes
  • radiological age assessment
  • identification of concealed objects within the body
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63
Q

IRMER17 duty holders

A
  • defines particular roles during medical exposures - a dentist may perform all these roles
  • referer
  • practitioner
  • operator
  • employer
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64
Q

IRMER17
define referer, practitioner, operator and employer

A
  • referer- puts in referral for imaging, provide sufficient medical data to practitioner to enable justification
  • practitioner - justifies the examination and may also authorise it, ensures doses ALARP and complies with procedures
  • operator - can authorise and carry out exposure, assesses and reports image to be provided to referrer
  • employer - must provide referral criteria
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65
Q

operator roles and responsibilities

A
  • person taking X-ray
  • person performing quality control on X-ray set
  • person cleaning film processor
  • person performing clinical evaluation
  • must be suitably trained
  • responsibilities: select equiptment and methods to limit dose
  • follow employers procedures
  • must not perform the exam unless authorised as justified
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66
Q

IRMER17
justification

A
  • carried out by practitioner taking into account info supplied by referrer
  • consider objectives, benefits and risks
  • justified exposure must then be authorised - recorded that the exposure is justified and may proceed
  • if practitioner cannot authorise then can be authorised by operator
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67
Q

a radiographic exam cannot legally proceed unless the justification process is complete therefore -

A
  • any requests with insufficient information/practitioner feels are not justified must be referred back to the referrer
  • exams must be authorised as justified before the exposure
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68
Q

what is radiographic optimisation

A
  • ensures exposures as ALARP - as low as reasonably practicable
  • responsibility of both practitioner and operator
  • selecting appropriate type of radiograph and equiptment
  • ensuring QA is carried out
  • assessing patient dose
  • adherance to diagnotic reference levels
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69
Q

what is an RPA and their role

A
  • radiation protection adviser
  • person meeting HSE (health and safety executive) requirements to advise on radiation safety
  • certificate issued by RPA2000
  • roles - regular equiptment checks, investigations, contingency plans
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70
Q

IRR17 specifies training that

A
  • staff operating X-ray units and working in and around controlled areas should recieve
  • may include basic radiation safety measures, specific requirements for that workplace
  • also specifies annual radiation dose limits for workers and members of public
  • dental staff dose levels should be far below dose limits of 6mSv/yr
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71
Q

what is a new requirement in IRMER17

A
  • for information to be given to patients about benefits and risks of the radiation exposure
  • information poster sufficient in many cases
  • “your Xray and you”
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72
Q

other names for panoramic radiography

A
  • dental panoramic tomogram DPT
  • orthopantomogram OPT/OPG
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73
Q

what is tomography

A
  • developed to allow “slice” of the subject to be viewed separately
  • 2 types in medical imaging
    1. conventional - 1 slice
    2. computed - multiple slices
  • can be produced using different phenomena - panoramic X-rays, CBCT, CT, MRI, PET
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74
Q

panoramic radiography basics
what is it a form of
how is it taken

A
  • form of conventional tomography - involves a modified version of linear tomography
  • captures a curved slice of the jaws which is then displayed as a flat image
  • patient stands in middle of machine
  • X-ray source and receptor rotated around head during exposure
  • source primarily behind pt, receptor primarily infront
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75
Q

linear tomography principles

A
  • X ray source moves in one direction while receptor moves in opposite direction
  • structures in a focal slice remain projected onto same point of receptor - will be distinguishable on image
  • structures outside this slice are continually projected onto different points of receptor - faint and spread out across image
  • this slice is called the FOCAL TROOUGH
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76
Q

focal trough in panoramics

A
  • focal trough slice is curved to mimic shape of average mandible
  • this is as a result of complex rotational movements of X-ray source and receptor around the pt - point of rotation is not constant
  • patient with non standard arch size/shape may have decreased image quality
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77
Q

focal trough thickness in panoramics

A
  • focal trough is the thin band where images appear adequaltely sharp
  • decreased sharpness as you move more buccally or lingually
  • focal through is thinner in the incisor region - related to speed of rotation at this point - blurry incisors not uncommon
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78
Q

focal trough limitations

A
  • ectopic teeth may be far enough out of focal trough
  • they might appear to be “missing”
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79
Q

what do orthogonal programmes on panoramics aim to provide
advantages and disadvantages

A
  • aim to provide X-ray beam angulation which is changed to be more orthogonal (closer to 90degrees) to the teeth
  • advantages - decreased overlap of teeth, aids assessment of approximal caries, more accurately represents interdental bone levels
  • disadvantages - distorts rest of skeleton to varying degrees, max sinus, mand rami etc
  • suitable for cases requiring only caries/perio bone loss assessment
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80
Q

magnification which occurs in panoramics in relation to focal trough

A
  • structures within focal trough magnified by approx 25%
  • structures lingual to focal trough increases magnification - teeth lingual to FT apper broader
  • structures buccal to focal trough decreases magnification - teeth buccal to FT appear narrower
  • effect is emphasised as distance from focal trough increases
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81
Q

describe vertical projection in panoramics

A
  • structures positioned further away from receptor will be projectd further up on image
  • this is due to angulation of the beam - always angled slightly upwards
  • typically 8 degrees above horizontal
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82
Q

panoramic positives and negatives vs periapical

A
  1. positives
    * can capture entire dentition in one image
    * able to image non dental areas - rami, condyles, max sinus
    * lack of intra-oral holders benefits some pts
  2. negatives
    * worse clarity - more superimposition and artefacts and worse resolution
    * longer exposure time - increased risk of movement
    * higher radiation dose per image
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83
Q

what can be used to reduce radiation dose for panoramic

A
  • field limitation
  • for example panoramic only capturing R side of mouth if only investigating R side
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84
Q

main components of panoramic machine

A
  • X-ray tubehead
  • receptor (usually digital)
  • control panel
  • patient-positioning apparatus
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85
Q

panoramic control panel common options

A
  • field size
  • arch size/shape
  • position of machine eg height
  • position of pt positioning aparatus
  • X-ray tube exposure factors
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86
Q

preparing pt for panoramic

A
  • remove metal foreign bodies from head and neck
  • position patient using positioning apparatus
  • advise pt to have tongue to roof of mouth, stand still and dont talk or swallow
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87
Q

patient positioning apparatus for panoramic

A
  • bite peg - pt into edge to edge occlusion
  • light beam markers - horizotal line to frankfurt plane, vertical mid-line matches mid-saggital plane, canine line match maxillary canines
  • head grabber
  • chin rest
  • arm handles for stability
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88
Q

how long does panoramic typically take

A

10-15 seconds

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89
Q

What is the error here

A

Frankfort plane not horizontal
Patient in chin down position
Gives smiling occlusal plane appearance

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90
Q

What is the error here

A

Frankfort plane not horizontal
Patient in chin up position
Occlusal plane flat appearance

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91
Q

What is the error here

A

Mid Sagittatal plane not centred
Distortion to one/both sides

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92
Q

What is the error here

A

Mid saggital plane not vertical
Distortion and occlusal plane cant

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93
Q

What is the error here

A

Patient slumped posture
Excessive cervical spine shown

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94
Q
A
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95
Q

types of misleading shawdows on panoramic radiographs

A
  • double shadow - created by structures near centre of rotation - captured twice due to central location….hyoid bone, soft palate, cervical spine etc
  • ghost shadow - created by structures between x ray source and centre of rotation - structures on one side projected higher onto other side…apears magnified and blurred
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96
Q
A
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97
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98
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A
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99
Q
A
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100
Q
A
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101
Q
A
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102
Q
A
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103
Q
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104
Q
A
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105
Q
A
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106
Q
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107
Q
A
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108
Q

charting from radiographs function

A
  • assess developing dentition, impacted teeth, missing teeth etc
  • evaluate existing restorations
  • investigate caries and other pathologies
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109
Q

normal eruption sequence by age

A
  • age 6 - 6s and mand 1s
  • age 7 - mand 2s and max 1s
  • age 8 - max 2s
  • age 11 - mand 3s and 4s, max 4s
  • age 12 - max 3s and 5s and 7s, mand 5s and 7s
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110
Q

systematic approach to radiographic interpretation
order

A
  1. overview
  2. teeth
  3. apical tissues
  4. periodontal tissues
  5. bone
  6. other structures
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111
Q

radiographic interpretation
overview

A
  • display issues
  • technical errors
  • general findings - normal outlines, approx age of pt
  • foreign bodies
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112
Q

radiographic interpretation
teeth

A
  • number
  • position
  • development
  • morphology
  • condition of crows and roots
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113
Q

radiographic interpretation
apical tissues

A
  • lamina dura - intact/lost
  • periodontal ligament space - normal, widened, irregular
  • abnormal radiolucencies/radiopacities around the apices
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114
Q

radiographic interpretation
periodontal tissues

A
  • periodontal bone levels
  • furcation involvement
  • crestal bone quality
  • PDL space
  • calculus deposits
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115
Q

radiographic interpretation
what to describe for a specific structure

A
  • site
  • radiodensity
  • shape
  • margins
  • size
  • multiplicity
  • relation to other structures
  • effect on other structures
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116
Q

radiographic interpretation
interpretation pitfalls

A
  • satisfaction of search - finding the thing you want and then stopping
  • tunnel vision - only assessing specific areas of interest
  • getting side tracked - focusing on an interesting finding and neglecting the rest
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117
Q

principles of radiation protection

A
  • justification
  • optimisation - ALARP
  • dose limitation - for radiation workers and members of public NOT patients
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118
Q

referer info required via trakcare to request radiographs

A
  • unique ID of pt - name, dob, CHI
  • clinical info to justify exposure
  • information on pregancy if relevant
  • unique identifying signature - trakcare captures dentist logged
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119
Q

requesting radiographs
pregancy considerations

A
  • urgency of exposure if involving abdominal or pelvic regions
  • in dentistry abdominal and pelvic regions not irradiated by primary beam
  • emotions of pt important - can delay if pt prudent
  • discuss with clinician and pt
  • inform radiology if requesting - note in trakcare request
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120
Q

how often to do bitewings based on risk status

A
  • high - 6 monthly
  • moderate - annually uless risk status alters
  • low - 12-18 months for primary, 2 yearly for permanent
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121
Q

requesting a ragiograph
how to on trakcare

A
  • completed by logged-in clinician
  • select type of radiographs required
  • complete clinical questions and answers - input relevant clinical info
  • use FDI notation when referring to teeth
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122
Q

electromagnetic spectrum
properties

A
  • no mass
  • no charge
  • always travels at speed of light
  • can travel in a vacum
123
Q

electromagnetic spectrum main groups in order of shorter to longer wavelength

A
  • gamma-ray
  • X-ray
  • ultraviolet
  • visible
  • infrared
  • microwave
  • radiowave
124
Q

electromagnetic spectrum
frequency

A
  • how many times the waves shape repeats per unit time
  • measured in hertz
  • one hertz = one cycle per second
125
Q

electromagnetic spectrum
wavelength

A
  • distance over which the waves shape repeats
  • measured in metres
126
Q

electromagnetic spectrum
speed

A
  • speed = frequency x wavelength
  • for all electromagnetic spectrum speed is at a constant 3 x 10^8 m/sec
  • therefore if frequency increases then wavelength must decrease
127
Q

photon energy measure

A
  • measured in electron volts eV
  • 1 eV = energy gained by 1 electron moving across a potential difference of 1 volt
  • energy is directly proportional to frequency
  • higher frequency = higher energy
128
Q

types of X-rays

A
  • X ray photon energies range from 124eV to 124thousand eV
  • hard X-rays (higher energies) able to penetrate human tissue
  • soft X-rays (lower energies) are easily absorbed
  • medical imaging mostly uses hard X-rays (eg >5k eV)
129
Q

properties of X-rays

A
  • form of electromagnetic radiation - no mass, no charge, very fast, can travel in vacuum etc
  • undetectable to human senses
  • man -made
  • cause ionisation - ie displacement of electrons from atoms/molecules
130
Q

describe the basic production of X-rays

A
  • electrons fired at atoms at very high speed
  • on collision kinetic energy of these elctrons are converted to electromagnetic radiation and heat
  • ideally converted to X-rays
  • X-ray photons aimed at a subject
131
Q

ground state atom and ionisation

A
  • an atom in its ground state is neutral - number of electrons = number of protons
  • ionisation - removing/adding electrons to an atom
132
Q

electron shells labelling and number of electrons in each shell

A
  • innermost shell is K, then L, M, N, O etc
  • maximum number of elctrons in each shell = 2 X n^2 (two times n squared)
  • n = number of the shell K=1, L=2, M=3 etc
133
Q

how are electrons held within shell and how are they removed

A
  • held in shell by electrostatic force - negative charge of electrons attracted to overall positive charge of the nucleus
  • to remove electron from its shell specific amount of energy required called binding energy
  • binding energy = additional energy required to exceed electrostatic force
134
Q

binding energy of electrons and what increases electromagnetic force

A
  • K shell electrons have the highest binding energy. then L, M etc
  • the closer the electron is to the nucleus the higher the electrostatic force
  • the more positively charged the nucleus the greater the electromagnetic force
  • binding energy measured in keV
135
Q

electrom movement between shells and energy

A
  • energy required to move an electron to a more outer shell = the difference in binding energies of the 2 shells
  • if electron drops to a more inner shell then this specific amount of energy is released - possibly in form of X-ray photons if sufficient energy
136
Q

what is current
measurement and direction

A
  • current is flow of electrical charge - usually by movement of electrons
  • measured in amp (A) - measure of how much charge flows past a point per second
  • direction is either direc or alternating current
  • direct current - constant unidirectional flow (D)
  • alternatic current - flow repetidly reverses direction (AC)
  • mains electricity is AC
137
Q

role of transformers and types

A
  • alter the voltage (difference in electrical potential between 2 points in electrical field) and the current from one circuit to another
  • 2 separate transformers required for X-ray unit
    1. mains to X-ray tube
    2. mains to filament
  • step up trasformer - increases potential difference across x-ray tube to 60-70kV and current milliamps mA
  • step down transformer - decreases potential difference across filament to 10volts 10amps
138
Q

rectification of current in X-ray

A
  • X-ray production requires a unidirectional current but X-ray units are powered by mains electriticy which is AC
  • x-ray units have genertors which modify the AC so that it mimics a constant direct current
  • process known as rectification
139
Q

dental x ray unit voltages

A
  • requires two different voltages
  • one as high as 10k volts
  • one as low as around 10volts
140
Q

intensity of X-ray beam

A
  • quantity of photon energy passing through a cross-sectional area of beam per unit time
  • to increase intensity increase the number and/or energy of photons
  • proportional to current in filament mA and potential difference across x-ay tube kV
141
Q

inverse square law

A
  • intensity of x-ray beam is inversely proportional to the square of the distance between X-ray source and point of measurement
  • doubling the distance will quarter the dose
  • 1 = intensity X distance^2
  • 1/ distance ^2 X prev intensity
142
Q

periapical setup for upper anteriors

A
  • blue kit
  • size 0 film
  • vertical
  • 1s and 2s in each side captured together - 11+12 together and 21+22 together
  • 3s own image
  • for upper anteriors where only 11/21 requested may be imaged together
143
Q

periapical setup for lower anteriors

A
  • blue kit
  • size 0 film
  • vertical
  • 41 and 31 together
  • 42 and 43 together
  • 32 and 33 together
144
Q

periapical setup for posterior teeth

A
  • yellow kit
  • size 2 film
  • horizontal
  • for deciduous molars size 0 horizontal
  • image 4s to 7s together - routinely 1 image per quadrant
  • 2nd radiograph per quadrant if 8s present 6s-8s
145
Q

bitewing setup

A
  • red kit
  • posterior images only
  • generally one image per side unless all premolars and molars present
  • size 2 horizontal
146
Q

patient positioning for OPT

A
  • arms on handle
  • rest chin on chinstand
  • mid saggital line on midline of face
  • frankfurt plane horizontal to floor - alar tragus line
  • canine line on canines
  • bite block with incisors
  • put tongue to roof of mouth
147
Q

What is this setup for

A

Anterior periapicals

148
Q

What is this setup for

A

Posterior periapicals

149
Q

What is this setup for

150
Q

xray tube components

A
  • glass envelope - vacuum inside
  • cathode -ve - filament and focusing cup
  • anode +ve - target and heat-dissapating block
151
Q

cathode filament
material & function

A
  • coiled metal wire made of tungsten - high melting point, high atomic number so lots of electrons per atom
  • low voltage, high current electricity passed through wire and heats up until approx 2200 degrees celcius
  • electrons are released from atoms in the wire by thermionic emission
  • cloud of electrons form around cathode
  • increase in current in filament increases the heat and no. if electrons
152
Q

cathode focusing cup
material & function

A
  • metal plate which is shaped around filament made of molybdenum
  • it is negatively charged so repels electrons released at filament
  • shaped to focus the electrons on the anode target
  • high melting point and relatively poor thermionic emitter
153
Q

cathode-anode relationship

A
  • electrons released at filament are repelled away from cathode (filament and focusing cup) and are attracted to the anode target
  • high voltage electricity passed through results in high potential difference between negative cathode and positive anode
  • increasing potential difference increases acceleration of speed electrons travel which then increases kinetic energy
  • electrons have high kinetic energy upon colliding with anode target
154
Q

x-ray tube glass envelope
material and function

A
  • air tight enclosure which supports cathode and anode
  • maintains a vacuum so electrons can travel from cathode to anode unhindered by gas molecules
  • leaded glasss to absorb x - ray photons - except for at un-leaded window
  • only the xray photons travelling in desired direction can escape from the x-ray tube
155
Q

anode target
material and function

A
  • metal block made of tungsten - high MP
  • bombarded by electrons and produces x-ray photons of useful energies &lots of heat
  • focal spot = precise area on target where electrons collide and Xrays are produced - ie the x-ray source
156
Q

anode heat dissapating block
material and function

A
  • target is embedded in a larger block of metal made of copper - high MP and high thermal conductivity
  • heat produced in target dissapates into this block by thermal conduction
  • reduces risk of overheating which could damage target
157
Q

desribe the penumbra effect

A
  • blurring of radiographic image due to focal spot not being a single spot
  • minimised by decreasing size of focal spot
158
Q

focal spot angulation
situation, problem and solution

A
  • situation - need a small focal spot
  • problem - heat released when kinetic energy converted to heat is 99% compared to 1% converted to x-ray photons
  • decreasing focal spot size increases heat concentration
  • solution - angled target to increase surface area where electrons impact (better heat tolerance) and decreases penumbra effect
159
Q

tubehead main components

A
  • X-ray tube
  • metal shielding - usually lead with window where x-ray beam exits
  • oil - dissapates heat produced by thermal convection
  • spacer come
160
Q

tubehead filtration
material and function

A
  • aluminium - minimum thickness required <70kV 1.5mm and >70kV 2.5mm
  • removes lower energy non-diagnostic x-rays from beam - as these would increase pt dose but not contibute to image
161
Q

tubehead spacer cone
function

A
  • ductates distance between focal spot of target and patient
  • focus to skin distance FSD
  • altering fsd will affect how much beam diverges - increasing fsd decreases divergence but also decreases maginfication of image
  • set distance to ensure consistent radiographic technique
  • also indicates direction of the beam - beam aiming device
162
Q

focus to skin distance for voltages

A
  • <60kV 100mm
  • > 60kV 200mm (modern equiptment)
  • measurement taken from focal spot (where x ray photons originate on target)
  • marked on tubehead
163
Q

collimator
material and function

A
  • lead diaphragm attached to end of spacer cone
  • reduces pt dose by cropping x-ray beam to match size and shape of x-ray receptor
  • change circular beam created to a rectangular
164
Q

consequences of electrons bombarding target

A
  • heat production - 99% of interactins and involve outer shell electrons of tungsten atoms
  • x-ray production 1% of interactions - involve inner-shell electrons and nuclei of tungsten atoms at target
165
Q

continuous radiation vs characteristic radiation

A
  • continuous - produce a continuous range of X-ray photon energies, maximum photon energy matches the peak voltage, bombarding electron interacts with nucleus of target atom
  • characteristic - produces specific energies of x-ray photon, characteristic to element used for target, photon energies depend on binding nergies of electron shells, bombarding electron interacts with inner-shell electrons of target atom
166
Q

characteristic radiation spectrum
photon energy equals

A
  • photon energy equals the difference uin the binding energies of the 2 shells involved - which are specific to element of target (tungsten)
  • K shell binding energy of tungsten = 69.5kV
  • dental x-ray tubes often operate at 70kV so that bombarding electrons have sufficient energy (70keV) to displace k shell electrons
167
Q

summary of beam leaving dental xray unit

A
  • stream of x-ray photons going in same direction - diverging but near parallel
  • ideally collimated to shape of receptor
  • lower energy photons removed by filtration
  • beam consists of continuous range of energies up to 70keV - with characteristic spikes around 49 and 67 keV
  • travel at speed of light until they interact with something
168
Q

photons can interact with matter in 3 ways

A
  • transmission - passes through matter unaltered
  • absorption - stopped by the matter, energy fully deposited into tissue
  • scatter - changes direction, deflected by tissue
169
Q

increasing voltage and current results in

A
  • increasing voltage - increases average photon energy and increases maximum photon energy
  • increasing current - increases number of photons
170
Q

describe attenuation and how it displays image

A
  • attenuation = reduction in intensity of x-ray beam as photons absorbed and/or scattered by tissue
  • indirectly leads to x-ray image due to tissues and materials having varying degrees of attenuation
  • minimal attenuation = black
  • partial attenuation = grey
  • complete attenuation = white
171
Q

types of specific attenuation interactions

A
  • photoelectric effect
  • compton effect
172
Q

specific attenuation interactions
photoelectric effect summary

A
  • photon in X-ray beam interacts with inner shell electron in subject
  • resulting in absorption of the photon and creation of photoelectron
  • photoelectron gets ejected
  • photoelectron can ionise (and potentially damage) adjacent tissues
  • vacancy in inner shell is filled by cascade of outer shell electrons - produces light and/or heat
173
Q

specific attenuation interactions
photoelectric effect occurs when

A
  • occurs when energy of incoming photon is equal to or just greater than binding energy of inner shell electron
  • this happens with lower energy photons as human tissues have relatively low binding energies
  • any excess photon energy becomes kinetic energy of photoelectron
174
Q

specific attenuation interactions
photoelectric effect results in what

A
  • prevents x-ray photons reaching the recepto
  • leads to lighter area on raduiographic image
175
Q

specific attenuation interactions
photoelectric effect probability calculation

A
  • p x Z^3 / E^3
  • p = proportional to physical density of material
  • E = photon energy
  • Z = atomic number
176
Q

specific attenuation interactions
photoelectric effect proportional to

A
  • proportional to atomic number cubed Z^3
  • small steps in Z result in large jumps in absorption
  • results in good contrast between differenyt tissues on radiographic image
177
Q

specific attenuation interactions
compton effect summary

A
  • photon in electron beam interacts with outer shell electron in subject
  • resulting in partial absorption and scattering of the photon and creation of recoil electron (another name for ejected electron)
  • recoil electron can ionise (and potentially damage) adjacent tissues
  • photon loses energy and scatters - can then undergo photoelectric effect and further compton effect interactions
178
Q

specific attenuation interactions
compton effect occurs when

A
  • occurs when energy of incoming photon is much greater than binding energy of electron
  • therefore seen with higher energy photons and outer shell electrons (which are loosely bound)
179
Q

specific attenuation interactions
compton effect - direction of scatter

A
  • can be deflected in any direction but are influenced by the energy of incoming photon
  • higher energy photons are deflected more forward - forward scatter
  • lower energy photons are deflected more backward - backward scatter
  • majority of scatter from x-ray beam at 70kV is forward scatter
  • scatter is the reason why controlled area needs to completely surround the pt
180
Q

specific attenuation interactions
compton effect on radiographic image

A
  • photons scattered backwards, sideways or very slightly obliquely forward will not reach the receptor - do not affect image
  • photons scattered slightly obliquely forward may still reach receptor but will interact with wrong area - cause darkening of image in wrong place - results in fogging of image which reduces image contrast/quality
181
Q

specific attenuation interactions
compton effect probability of occurance

A
  • proportional to density of material
  • independent of atomic number
  • weakly proportional to photon energy - increasing photon energy has minimal effect on likelihood of compton effect but higher energy photons more likely to scatter forwards and reach receptor
182
Q

how to reduce scatter with collimation

A
  1. decreases surface area irradiated
  2. decreases volume of irradiated tissue
  3. decreased number of scattered photons produced in the tissue
  4. decreased scattered photons interacting with receptor
  5. decreased loss of contrast on radiographic image
183
Q

compton & photoelectric effect impact on radiation dose

A
  • photoelectric effect results in depostion of all x-ray photon energy into tissue - therefore increases pt dose but this is necessary for image formation
  • compton effect there is some deposition of x-ray photon energy into tissue - therefore increases patient dose - but scattered photons do no contribute usefully to image and may increase dose to operators from back scatter
184
Q

effect of lowering kV on x-ray unit

A
  • lower x-ray tube potential difference results in overall lower energy photons produced
  • this increases photoelectric effect interactions and increases contrast between tissues with different Z (atomic number)
  • but increases dose absorbed by pt
185
Q

effect of raising kV of x-ray unit

A
  • higher x-ray tube potential difference so overall higher energy photons produced
  • this decreases photoelectric effect interactions and increases forward scatter
  • decreases dose absorbed by pt
  • but decreases contrast between tissues with different Z
  • decision is compromise between image quality and pt radiation dose - uk guidance advises 60-70kV for IO
186
Q

comparison of interactions in X-ray process

A
  • continuous radiation interaction & characteristic radiation interaction - occurs at target in tube and electrons are interacting with tungsten atoms - leads to production of x-ray photons
  • photoelectric & compton effect - occur in pt/receptor/shielding and x-ray photons interacting with atoms - lead to attenuation of x-ray beam
187
Q

types of radiation

A
  • alpha particle (2 protons/2 neutron) - large particle travels few inches
  • beta particle (electron) - very small particle travels a few feet
  • gamma ray - high energy travels long distances
  • X rays - high or low energy travels long distances
188
Q

ionising radiation has enough energy to

A
  • turn atoms into ions
  • it does this by knocking away electrons orbiting the nucleus of an atom

`

189
Q

ionising radiation
interaction of radiation with matter

A
  • when radiation passes through matter it will ionise atoms along its path
  • each ionisation process will deposit a certain amount of energy locally - approx 35eV
  • this energy is greater than the energy involved in atomic bonds - eg ionic and covalent bonds approx 4eV
190
Q

most significant effect of ionising radiation

A
  • damage to DNA - evidence of DNA damage can be seen in the faulty repair of chromosome breaks
  • seen in individuals who are exposed to large doses
  • majority of damage is easily repaired, depending on the category of damage
191
Q

dose survival curves

A
  • low doses of radiation produce less damage
  • alpha particles have a linear relationship - increasing dose kills more cells
  • alpha particles kills more cells than a similar dose of X-rays would
192
Q

dose rate

A
  • radiation delivered at a low dose rate is less damaging - cells can repair less serious DNA damage before further damage occurs
  • at high dose rates the DNA repair capacity of the cell is likely to be overwhelmed
193
Q

types of DNA damage

A
  • direct - radiation interacts with the atoms of a DNA molecule or another important part of the cell
  • indirect - radiation interacts with water in the cell - producing free radicals which can cause damage
194
Q

single vs double strand DNA damage

A
  • single strand break in DNA can usually be repaired
  • double strand breaks are more difficult to repair - usually occur as a result of alpha radiation
  • if double strand DNA repair is faulty this can lead to mutations which can affect cell function
195
Q

DNA damage and repair
biological effect will depend on

A
  • number of factors
  • type of radiation
  • amount of radiation (dose)
  • time over which the dose is recieved (dose rate)
  • tissue or cell type irradiated
196
Q

large radiation exposure
organ cancer risks

A
  • following large radiation exposure only higher incidences of cancer in certain tissues
  • risk will vary depending on the organ that recieves the highest dose
  • organ risks - oesophagus, thyroid, lungs, skin, breast, stomach, liver, colon, gonads
197
Q

radiosensitivity of tissues dependant on 2 factors

A
  1. the function of the cells that make up the tissues
  2. if the cells are actively dividing
198
Q

what type of cells very radiosensitive vs what type less sensitive

A
  • stem cells are very radiosensitive - divide frequently and exist to produce cells for another cell population
  • differentiated cells are less sensitive to radiation damage - do not exhibit mitotic behaviour
199
Q

what type of tissue is highly radiosensitive vs least radiosensitive

A
  • more rapidly a cell is dividing the greater the sensitivity to radiation
  • highly radiosensitive - bone marrow, lymphoid tissue, GI, gonads, embryonic tissue
  • moderately - skin, vascular endothelium, lung, lens of the eye
  • least - CNS, bone and cartilage, connective tissue
200
Q

dose is a measure of

A
  • the amount of energy that has been transferred and deposited in a medium
  • amount of radiation absorbed by human tissue
201
Q

dose quantities
absorbed dose

A
  • measures the energy deposited by radiation
  • has units of gray (Gy)
202
Q

dose quantities
equivalent dose

A
  • absorbed dose multiplied by weighting factor - depending on the type of radiation
  • for beta, gamma and Xrays the weighting factor is 1
  • for alpha particles the weighting factor is 20
  • has units of sieverts (Sv)
203
Q

LNT model

A
  • linear no threashold model
  • stimates the long term biological damage from radiation
  • it assumes the damage is directly proportional (linear) to radiation dose
  • it assumes radiation is always harmful with no safety threshold
  • several small exposures would have the same effect as one large exposure - this is known as response linearity
204
Q

two type of radiation effects

A
  • deterministic effects - tissue reactions only occur above a certain dose and severity of effect related to dose
  • stochastic effects - probability of occurrence is related to dose recieved
205
Q

type of radiation effects
deterministic effects

A
  • tissue reactions only occur above a certain dose and severity of effect related to dose
  • unusual to see in radiology
  • often effects will not show immediately - several days after exposure
  • examples - bone marrow cell depletion, cateracts, sterility, hair loss, skin damage
  • lethal dose 6Sv to whole body
206
Q

type of radiation effects
stochastic effects

A
  • probability of occurrence is related to dose recieved
  • no known threshold for stochastic effects - no dose below which effect will not occur
  • cannot predict if these effects will occur in exposed pt or severity
  • likelihood of effect occuring increases as dose increases
  • effects can develop years after exposure
  • effects subdivided into two categoris - somatic (result in disease) or genetics (abnormalities in descendents)
207
Q

natural backround radiation sources

A
  • cosmic rays
  • internal radionuclides from diet
  • radionuclides in the air eg radon
  • external gamma radiation eg soil, rocks
  • air travel
  • annual background radiation dose is 2.2mSv
208
Q

radiation effect of pregnancy

A
  • exposure could damage or kill enough of the cells for the embryo to undergo resorption
  • lethal effects caused by doses before or immediately after implantation of embro in uterus
  • during organogenesis (2-8weeks) doses >250mGy could lead to growth retardation
  • doses for these abnormalities more than 1000 times greater than that of IO X-ray
209
Q

methods to reduce patient dose

A
  • use E speed film or faster - fewer X-ray photons required
  • use a kV range of 60-70kV
  • focus to skin distance should be >200mm
  • use rectangular collimation
210
Q

diagnostic reference levels
what are they and why we have them

A
  • established dose levels for typical examintions for standard sized patients
  • used so individual X-ray units can be compared to DRL and national reference levels
  • enables identification of units giving higher doses
214
Q

in dental X-ray tube what is used for focusing cup

A

molybdenum

215
Q

which of these is measure in grays
absorbed dose, effective dose or equivalent dose

A

absorbed dose

216
Q

type of radiation effect we are concerned about in dental radiography

A

somatic non-deterministic
??? unsure go over

217
Q

what is the most common mechanism by which x-ray photons cause carcinogenesis

A

indirect damage to DNA

218
Q

what model do we use to estimate the risk of stochastic effects

A

linear no threshold model

219
Q

at least how far should you be from the X-ray source and pt when radiographing

A
  • 1.5m
  • never tand directly in the line of the primary bea,
220
Q

X-ray receptors used
digital vs film

A
  • digital - phosphor plate or solid-state sensor (all multiple use)
  • film - direct action film or indirect action film (all single use)
221
Q

x-ray shadow creating image

A
  • X-ray shadow created when x-ray beam passes through an object and some of the photons are attenuated
  • image receptor detects this x-ray shadow and uses it to create an image
222
Q

digital radiography
what does the receptor measure

A
  • receptor measures x-ray intensity at defined areas - arranged in a grid
  • each area given value relating to intensity - typically from 0-255
  • each value corresponds to a different shade of grey
  • 0=black
  • 255=white
223
Q

digital radiography
digital image displayed as

A
  • grid of squares called pixels
  • more pixels = better details = higher resolution
  • each pixel can only display one colour at a time
  • each digital image will require more stoarage space = increased cost
224
Q

digital radiography
greyscale bit depth

A
  • radiographs typically processed in at least 8 bits
  • bits refers to the number of different shades of grey available
  • 8 binary digits = 2^8 = 256 = 256 shades of grey
225
Q

digital radiography
manipulating digital images

A
  • software can be used to copy, resize and alter images
  • original, negative, emboss, contrast/windowing, magnify
226
Q

format for digital images

A
  • digital imaging & communications in medicine - DICOM
  • international standard for handling digital medical images
  • used to transmit, store, retrieve, print, process & display images
  • an alternative to JPEG, GIF etc
  • allows imaging to work between different software, machines, manufacturers, hospital etc
227
Q

management of digital images

A
  • PACS
  • picture archiving and communication system
  • technology which provides storage and access to images
  • varies in size/scale - in Scotland natiowide hospital PACS, in England separate hosptial PACS for each trust
228
Q

PACS main components

A
  • input imaging modalities - X-ray, CT, MRI etc
  • secure network for the transmission of pt info
  • workstations for interpreting & reviewing images
  • archives for the storage and retrieval of images and reports
229
Q

best way to view digital radiographs

A
  • environment - subdued lighting and avoid glare
  • monitor - clean, gd display resolution, high enough brightness level, suitable contrast level
230
Q

types of digital IO receptor

A
  • phosphor plates - not connected to computer and to be put in scanner to create final image
  • solid state sensors - connected to computer usually wired but can be wireless and image created and read within sensor itself so created virtually instantly
231
Q

types of solid state sensor

A
  • CCD - charge-coupled device
  • CMOS - complimentary metal oxide semiconductor
232
Q

what can be used to assess resolution, contrast and brightness of monitor

A
  • SMPTE test pattern
  • society or motion picture and television engineers
  • available online
233
Q

image creation using phosphor plates

A
  • within the patients mouth
    1. receptor exposed to x-ray beam
    2. phosphor crystals in receptor excited by x-ray energy resulting in creationof LATENT IMAGE
  • within the scanner
    1. receptor scanned by laser
    2. laser energy causes the excited crystals to emit visible light
    3. light is detected and creates the digital image
234
Q

phosphor plates vs solid state sensors
phosphor plates

A
  • thinner, lighter and more flexible
  • wireless - more stable
  • variable room-light sensitivity - risk of impaired image
  • latent image needs to be processed in scanner seperately
  • handling similar to film
235
Q

phosphor plates vs solid state sensors
solid-state sensors

A
  • bulkier and rigid
  • usually wired
  • smaller active area
  • no issues with room-light control
  • more durable - replaced less often
  • more expensive
236
Q

cross-infection control for IO receptors

A
  • IO receptors have single-use covers to prevent saliva contamination
  • example - adhesive sealed plastic covers for phosphor plates
  • long plastic sleeves for wired solid state sensor
  • receptor still disinfected between uses
237
Q

radiographic film summary

A
  • material in which actual image is formed
  • sensitive to both x-ray photons and visible light photons
  • photons interact with emulsion on film to produce latent image
  • latent image only becomes visible after chemical processing
238
Q

radiographic emulsion comprised of

A
  • silver halide crystals - embedded in a gelatin binder (protective coating)
  • crystels are microscopic and are what eventually become “pixels” of final image
  • film generally higher resolution than digital
239
Q

radiographic emulsion
silver halide crystels how they work

A
  • usually silver bromide
  • become sensitised upon interaction with x-ray (and visible light) photons
  • during processing sensitised crystels converted to particles of black metallic silver = darker parts of final image
  • non-sensitised crystels removed = light parts of final image
240
Q

film speed

A
  • relates to amount of X-ray exposure required to produce an adequate image
  • increasing speed decreases radiation required to achieve an image
  • affected by numberand size of silver halide crystals - larger crystals = faster film but poorer image quality
  • example E is twice as fast as D = therefore requires half exposure time = half radiation dose
241
Q

when are intensifying screens used

A
  • used alongside special indirect action film for EO radiographs
  • too bulky for intra-oral use
  • indirect action film placed inside cassette with an intensifying screen on either side
  • screens release visible light upon exposure to x-rays and the visible light creates latent image on films
  • reduces radiation dose - but also reduces detail
242
Q

film processing common steps

A
  1. developing - converts sensitised crystals to black metallic silver particles
  2. washing - removes residual developer solution
  3. fixing - removes non-sensitised crystals and hardens emulsion
  4. washing - removes residual fixer solution
  5. drying - removes water so that film is ready to be handled/stored
  • must be carried out in dark room with absolute light tightness and adequate ventilation
243
Q

self-developing films advantages and disadvantages

A
  • advantages - no darkroom or processing facilities required, faster
  • disadvantages - poorer image quality, relatively expensive, image deteriorates more rapidly over time
  • not recommended
244
Q

film radiography
describe automated cycle and benefits

A
  • all necessary film processing steps carried out within a machine
  • exposed film goes in one end - processed film comes out the other
  • faster and more controlled than manual processing and avoids need for a dark room
  • but more expensive
245
Q

film radiography
processing issues with developing

A
  • involves chemical reaction of sensitised silver halide crystals –> black silver
  • reaction time affected by temp, time and solution conc
  • developer solution oxidises in air so becomes less effective over time
  • developer solution needs to be replaced regularly
246
Q

potential causes of pale image

A
  • exposure issue - radiation exposure factors too low
  • developing issue - film removed from solution too early, solution too cold, solution too dilute/old
  • note! opposite will result in dark image
247
Q

film radiography
processing issues with fixing and washing

A
  • fixing involves chemical reaction which removes non-sensitised crystals and hardens remaining emulsion
  • inadequate fixing means non-sensitised crystals are left behind
  • image greenish-yellow or milky
  • image becomes brown over time
  • washing - developer and fixer solution will continue to act if not washed off
248
Q

digital radiography advantages vs film

A
  • no need for chemical processsing
  • easy storage and archiving of images
  • easy back-up of images
  • images can be integrated into pt records
  • easy transferring/sharing of images
  • images can be manipulated
249
Q

digital radiography disadvantages vs film

A
  • worse resolution - risk of pixelation
  • requires diagnostic level computer monitors
  • risk of data corruption/loss - solved by backing up
  • hard copy printouts generally have reduced quality
  • image enhancement can create misleading images
252
Q

common types of extra-oral radiographs

A
  • panoramic
  • cephalometric - lateral & postero-anterior
  • oblique lateral radiographs
  • skull radiographs - occipitomental, postero-anterior skull/mandible, true lateral, reverse towne’s
253
Q

extra-oral radiograph terminology

A
  • lateral = beam aimed at side of head
  • postero-anterior =beam starting posterioly and passing anteriorly
  • true = perpendicular to head
  • oblique = not perpendicular to head
  • occipitomental = through occipit and then mental region
254
Q

purpose for extra-oral radiograph

A
  • imaging larger sections of the dentition
  • alternative when pt is unable to tolerate intra-oral radiography
  • imaging non-dentoalveolar regions
255
Q

reference lines

A
  • mid-saggital plane - line down middle of face
  • interpupilary line - connects both pupils
  • frankfort plane - connects infraorbital margin and superior border of external auditory meatus (clinically use top of curl of nose)
  • orbitomeatal line - connects outer canthus and centre of external auditory meatus
  • note - 10 degrees difference between orbitomeatal and frankfurt plane
256
Q

cephalometry
use/clinnical applications

A
  • the measurement and study of the head
  • uses many different points, angles and distances to analyse anatomy
  • must be standardised and reproducible
  • clinical applications - orthodontics and orthognathic surgery
257
Q

lateral cephalogram type of radiograph and main anatomy shown

A
  • standardised, true lateral skull radiograph
  • taken using specialised equiptment
  • main anatomy - teeth, facial bones, soft tissues, paranasal sinuses, pharyngeal soft tissues, cervical vertebrae
258
Q

lateral cephalometry uses

A
  • assessing skeletal discrepancy - when functional or fixed appliacnes are to be used for labio-lingual movement of incisors
  • aiding location and assessment of unerupted/malformed teeth
  • give an indication of upper incisor root legnth
  • used at different stages - diagnosis, tx planning, monitoring progress, appraisal of tx results
259
Q

cephalostat function

A
  • all lateral ceph equiptment will have a cephalostat
  • ensures standardised positioning of equiptment and patients head - avoids discrepancies and reduces distortion of image
  • holds head at correct angle and stabilises to prevent movement
  • establishes correct distances between x-ray focal spot, pt and receptor
260
Q

lateral cephalogram standardised distances

A
  • receptor should be 1.5 - 1.8m from the x-ray focal spot to minimise magnification
  • keeping distances consistent ensures images taken at any time are directly comparable
261
Q

lateral ceph soft tissues probelm/solution

A
  • visualisationof soft tissue profile can aid pt management
  • problem - soft tissues show up poorly when exposure settings are optimised for hard tissues
  • solutions - depends on type of unit
    1. place an aluminium wedge filter in the unit to attenuate the specific area of the beam exposing facial soft tissues OR
    2. use software to enhance soft tissue post-exposure
262
Q

extra-oral collimation

A
  • field of view should not be bigger than what is clinically required
  • different options availabel depending on unit
  • units that do not use solid state sensor should also have triangular collimation to reduce exposure of the cranium
263
Q

CBCT benefits for cephalometry and disadvantages

A
  • no superimposition or magnification of anatomy
  • images can be viewed at any angle
  • disadvantage - not indicated currently as additional info gained is not clinically significant enought to justify increased dose
264
Q

CBCT benefits for orthognathic surgery

A
  • commonly used to aid pre-operative assessment and treatment planning
  • due to better visualisation of anatomy
265
Q

lateral cephalometry patient contact shielding

A
  • thyroid collar almost always used as thyroid gland is radiosensitive
  • may obscure hyoid bone and cervical vertebrae - irrelevant to majority of cases but sometimes used to assess maturity of skeleton
266
Q

oblique lateral radiograph provides

A
  • provides view of posterior jaws without superimposition of contralateral side
  • useful if pt unable to tolerate IO radiogrpahs and unable to sit still in panoranic unit
  • uncommon nowadays as difficult technique and panoramic superseeds in most situations
267
Q

oblique lateral radiograph indications

A
  • alternative for when IO or panoramic radiographs contraindicated in pt - pre-cooperative children, learning difficulties, involuntary movements (tremors), unconscious
  • indications similar to panoramic radiography - assessment of dental pathology ; presence/position of unerupted teeth ; detection of mandibular fractures ; evaluating lesions affecting jaws
270
Q

what aspects should quality assurance programme cover

A
  • should cover ALL aspects of using radiographs
  • staff training
  • equiptment
  • patient dose
  • image processing
  • display equiptment
  • image quality
271
Q

quality assurance of digital image receptors
frequency and things to check

A
  • should be formally checked on a regular basis - at least every 3 months
  • things to check :
    1. the receptor itself
    2. image uniformity
    3. image quality
272
Q

receptor damage type affecting image
phosphor plates

A
  • scratches - white lines
  • cracking (from flexing) - network of white lines
  • delamination - white areas around edge ie separation of phosphor layer from base plate
273
Q

receptor damage type affecting image
solid state sensors

A
  • sensor damage - white squares/straight lines
  • dont tend to get issues as all sensor parts enclosed in sturdy material
274
Q

receptor damage type affecting image
film

A
  • aften appears as black marks due to sensitisation of silver halide crystals in radiographic emulsion
  • however may appear white iff emulsions scraped off
275
Q

digital image receptor checks

A
  1. the receptor
    * check for visible damage to casing/wiring
    * check if clean
  2. image uniformity
    * expose receptor to unattenuated x-ray beam and check image is uniform
    * should have consistent shade of grey across the whole image
  3. image quality
    * take radiograph of test object
    * assess the resulting image against a baseline
276
Q

name type of test object used to check image quality and how it works

A
  • step wedge - wedge with overlapping laters of lead foil
  • exposed to a normal clinical exposure and resulting image is compared to baseline
  • must be able to differentiate each layer
  • carried out refularly - eg every morning
  • each layer has different attenuation due to varying thickness of lead
277
Q

quality assurance of clinical image quality
3 parts

A
  1. image quality rating - grading each image
  2. image quality analysis - reviewing images to calculate success rate
    * identify any trends for suboptimal images
    * carried out periodically - every 4 months review last 150 images
  3. reject analysis - recording and analysing each unacceptable image
278
Q

quality ratings and targets

A
  • diagnostically acceptable (A) - not less than 95% (digital) not less than 90% (film)
  • diagnosically not acceptable (N) - not greater than 5% (digital) not greater than 10% (film)
279
Q

diagnostically acceptable positioning factors
bitewings

A
  • show enitre crowns of upper and lower teeth
  • include distal aspect of canine and mesial aspect of last standing tooh
  • may require >1 radiograph
  • every appproximal surface shown at least once without overlap - may be impossible if crowding
  • adequate contrast, shrpness and resolution, minimal distortion
280
Q

diagnostically acceptable positioning factors
periapical

A
  • shows entire root
  • shows periapical bone
  • shows crown
  • adequate contrast, sharpness, resolution, minimal distortion
281
Q

fault analysis and potential faults for radiographs

A
  • identifying and analysing faults so that they can be remedied
  • too dark or pale
  • inadequate contrast
  • unsharp
  • distorted
  • over-collimated
  • receptor marks/damage
282
Q

collimation error

A
  • incorrect assembly of receptor holder
  • “cone cutting”
  • incorrect alignment between xray tube and receptor holder
  • incorrect orientation of the rectangular collimator
283
Q

incorrect image radiodensity
potential causes

A
  • results in image too dark or too light
  • exposure factors - incorrect exposure settings, pt tissue toot thick, faulty timer on x-ray unit
  • developing factors (film) - incorrect duration, incorrect temperature, incorrect concentration
  • viewing factors - inappropriate light source (film), inappropriate display screen (digital), excessive environmental light
284
Q

need for radiographic localisation

A
  • to determine location of a structure or pathological lesion in relation to other structures
  • to help with tx plan
  • only needed where clinical examination insufficient to provide answer
285
Q

clinical situations where radiographic localisation required

A
  • position of unerupted teeth and proximity to important structures
  • location of roots/root canals
  • relationship of pathological lesions
  • trauma
  • soft tissue swellings - tissue/source
286
Q

options for viewsat right angles

A
  • panoramic and lower true occlusal
  • paralleling periapical and lower true occlusal
  • CBCT - each of the MPRs is at right angles to the others
287
Q

methods of radiographic localisation

A
  • normally two views required
  • views at right angles in their projection geometry
  • views with any different projection
  • with the aid of opaque objects -eg gutta percha point into sinus tract etc
  • anatomical knowledge crucial
288
Q

describe parallax

A
  • 2 radiographs taken at differemt position/angulation for radiographic localisation
  • will show an apparent change in the position of an object - caused by a real change in the position of the observer
  • example if you mmove to the right more lingual objects move to the right - same direction
  • more buccal objects move opposite way
289
Q

parallax mneumonic

A
  • Same Lingual Opposite Buccal - SLOB
  • PAL - my pal goes with me
290
Q

sequence of events for parallax if identifying X

A
  1. identify direction of tube movement
  2. establish what is X - what are we trying to know location of
  3. choose a reference
  4. observe movement of X against reference - if moves in same direction as tube movement object is lingual/palatal
291
Q

parallax localisation options
horizontal tube shift

A
  • 2 periapicals
  • 2 bitewings
  • 2 oblique occlusals
292
Q

parallax localisation options
vertical tube shift

A
  • panoramic and oblique occlusal
  • panoramic and lower (bisecting angle) periapical
293
Q

Causes of receptor damage

294
Q

Is the supernumerary buccal or lingual

A

It is lingual

295
Q

Which way to move tubehead to view buccal root

296
Q

solid state sensor vs phosphor plate key comparison

A
  • quicker to provide final imahe
  • more durable for handling
  • bulkier
  • usually wired
  • more expensive
  • less comfortable for pt
297
Q

film processing common steps

A
  1. developing - converts sensitised crystals to black metallic silver particles
  2. washing - removes residual developer solution
  3. fixing - removes non-sensitised crystals and hardens emulsion
  4. washing - removes residual fixer solution
  5. drying - removes water so that film is ready to be handled/stored
298
Q

under exposure of film results in

A

lighter image

299
Q

developer solution too warm/concentrated results in

A

darker image

300
Q

developer solution too old results in

A

lighter image

301
Q

film left in developer solution too long results in

A

darker image

302
Q

inadequate fixation of film results in

A

contrast of image reduced

303
Q

film exposed to visible light before processing results in

A

darker image

304
Q

processed film appears greenish and browns over time due to

A

inadequate fixation

BDS3 - CDS (13 decks)

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